Ariadne immediately puts him at the top of her mental List. After all, he's closest to her in age out of the whole group.
But as she gets to know him, she becomes aware that he is light-years ahead of her. He's smart. He's a grown man, set in his ways. Methodical, professional, cool. She is a graduate student who considers a khaki skirt 'business casual'.
She knows he's good-natured, even if he doesn't smile much. She relishes the rare smirk he allows when Eames cracks a particularly distasteful joke, or when she watches her favorite movie musicals online during late nights at the warehouse. She sometimes hears him humming along with the soundtrack, and it makes her blush-why should she be so tense about a guy who hums showtunes? Clearly he's just a softy who likes Rodgers and Hammerstein as much as she does.
But when he steals a kiss from her, she knows she's out of her depth.
And she likes it.